This invention relates to a scroll type fluid displacement apparatus, and more particularly, to a method for manufacturing the scroll and a tool used in the method.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 (Creux) discloses a device including two scrolls, each having a circular end plate and a spiroidal or involute spiral element. Both scrolls are maintained at an angular and radial offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of orbital motion, scroll type fluid displacement apparatus are applicable to compress, expand or pump fluids.
FIG. 1 of the drawings illustrates a basic design of a scroll suitable for use in a scroll type fluid displacement apparatus. Scroll 1 includes circular end plate 2 and a wrap or involute spiral element 3 affixed to or extending from one end surface of circular end plate 2. A scroll type fluid displacement apparatus includes a pair of such scrolls which are maintained at an angular and radial offset so that they interfit to form a plurality of line contacts to define at least one pair of fluid pockets. In such apparatus, each sealed off fluid pocket is defined by the line contacts between interfitting spiral elements and the axial contacts between the axial end surface of each spiral element and the inner end surface of the end plate of the other scroll. Thus, the volume of the fluid pockets is defined by the line contacts and the axial contacts.
The scroll is generally formed from pieces of metal by a machining process, such as milling. However, a milling process not only consumes a great deal of time and energy, but also produces large quantities of waste metal. If the scroll is formed by casting or forging, in the event the axial dimension of the spiral element must be made relatively long to obtain a large volume of high capacity, then the draft angle of the mold must be large. After the scroll is formed in such a mold, the spiral element must be machined to obtain uniform wall thickness which again results in relatively large quantities of waste metal. The latter manufacturing method also consumes a great deal of time and energy and this method makes it difficult to attain high accuracy of the wall dimensions of the spiral element.